1. Field of the Invention
The present invention relates generally to a mounting device which is used to support an automative power unit (engine and transmission) on a vehicle chassis and more specifically to a control arrangement which varies the mounting device rigidity in response to the status of a lock-up clutch included in an automotive power unit T/C (torque converter) unit.
2. Description of the Prior Art
JP-A-62-17440 discloses a mounting arrangement the rigidity of which can be varied by controlling the flow restriction between two fluid filled chambers. JP-A-62-20929 discloses an engine mount wherein the chamber arrangement is filled with an electrorheopectic fluid and the rigidity of the mount varied by applying a voltage across electrodes disposed in the chamber.
As rigidity of these types of mounts can be readily controlled, they have found application in supporting automotive power units on vehicle chassis. For example, the vibration which is produced when the engine is idling, the vibration is produced by the irregularites in the road surface which tend to be transmitted back to the engine, or engine shake type vibration, can be effectively controlled by varying the rigidity of the mount and thus varying the vibration transmission efficiency of the device. This of course permits the amount of vibration which is transmitted to the chassis to be reduced.
However, the vibration which is transmitted to the vehicle chassis is not limited to that which is produced by the engine. In the case an automatic transmission is provided with a lock-up clutch, it has been found that when said clutch is locked-up, reverberation causing vibration is transmitted from the transmission per se via the engine mounts to the chassis.
That is to say, when lock-up takes place in the manner disclosed in JP-A-62-137467, the lock-up clutch which is included in the torque converter is such as to transmit the engine torque directly to the transmission. On the other hand, when the lock-up clutch is released the torque is transmitted by way of the torque converter. When used alone the torque converter inherently smooths the torque transmission between the engine and the transmission in a manner which attenuates the tendency for the transmission to be excited by the vibration from the engine.
However, it has been found with this conventional type of lock-up control that when the lock-up arrangement is fully engaged and accelerator pedal is subject to sharp changes in the amount of depression, spikes in the transmission output shaft torque (see peaks P and Q in FIG. 15) tend to be produced. Further, as shown in FIG. 16, during fully locked up modes of operation, given that the rigidity of the engine mounts remains unchanged, the reverberation noise level in the vehicle cabin tends to undergo an undesirable increase.
On top of this, during partial lock-up clutch engagement or "slip lock-up" as it will be referred to hereinafter, the transmission output torque tends to fluctuate in the manner shown in FIG. 17 and brings about a phenomenon referred to as "lock-up jitter" J. This accordingly causes the transmission per se to vibrate in a manner which establishes another mode in which vibrational energy can be transmitted to the vehicle chassis.
Thus, although the above types of mount have been able to adequately control engine idling and shake types of vibration, the effects on noise generating vibration by the lock-up clutch has not yet been given any consideration and the isolation of the vehicle occupants from this type of problem has accordingly been wanting.